This invention is related to an adjustable annular prosthesis for use in the surgical correction of defects in the atrioventricular orifices, i.e. the mitral valve and the tricuspid valve. One of the most frequent causes of such defects is rheumatic fever, which can produce the retraction and consequent alteration of the atrioventricular orifices. They may also be caused by a bacterial inflammation of the heart known as endocarditis, be effected in the final phase of syphilis or arterial sclerosis, or be congenital.
Artrioventricular orifice defects are of two general types, which may be present separately or together. A narrowing of stenosis, for example of the mitral valve connecting the left auricle and the left ventricle, causes accumulation of blood in the left auricle, as a result of which the heart cannot operate efficiently. On the other hand, if the mitral valve does not close, some of the blood in the left ventricle flows back into the left auricle when the ventricle contracts, thus generating a condition known as valvular insufficiency. Mitral insufficiency is the defective closing of the mitral valve. Once established, it is a progressive disease.
The heart attempts to compensate for these atrioventricular orifice defects by hypertrophy, followed by dilation with enlargement of the cavities. The common symptoms are shallow respiration and palpitations under stress.
The distension of the auricular cavity and the valvular insertion region caused by valvular insufficiency increases the inefficiency of the valves, thus increasing regurgitation. A vicious cycle is established which must be interrupted in order to avoid the progressive deterioration of the patient.
Numerous techniques of plastic surgery have been developed for the conservative treatment of atrioventricular orifice defects. The best long-term results have been provided by annuloplasty with support by unstretchable rings, some non-deformable and others flexible.
Most of the annular prostheses used up to now are of an unchangeable caliber, in which effective correction depends to a great extent on the skill employed in the distribution of the suture. The functional result can only be verified at the end of the operation, that is to say when the result can no longer be changed without recourse to replacement of the prosthesis.
As a result, errors by way of excess are frequently committed by selecting excessively large diameters because of the suspicion of a stenosis, or excessively small diameters in search of greater security.
Taking into account the fact that a corrective operation on either the mitral valve or the tricuspid valve between the right auricle and right ventricle, the structures of which valves are similar, requires complex and fatiguing work on the part of the surgical team resulting in a risk to the patient which increases with the duration of the operation, there is fully understood the serious drawback represented by replacement of the prosthesis when a mistake due to too large or too small a size is noted after completion of the operation.
There is no doubt that the solution to the problem in question resides in being right at the start, that is in implanting an annuloplasty which provides a perfect fit so that subsequent correction is not necessary. However, since this is not a matter which can be measured a priori without skillful execution, such a fit, aside from pure accident, will only be obtained if the prosthesis is adjustable. However, a mitral or tricuspid insufficiency does not occur uniformly or, stated differently, the defective closing is zonal and irregular. Therefore it does not suffice to provide a ring whose diameter is reducible, but it is necessary that the ring be adjustable in such a manner that its radius is modified in those arcuate zones or sectors in which the defect is present.
U.S. Pat. No. 4,042,979 discloses an adjustable annular valvuloplasty ring that can be used to alleviate certain of the above-mentioned difficulties. The structure of this prior art article is, however, substantially different from that of the annular prosthesis of the present invention.